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Review reviewHigh

CVE-2026-26278

NaturalIntelligence fast-xml-parser, Red Hat Advanced Cluster Security 4.8, Red Hat Advanced Cluster Security 4.9

fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. In versions 4.1.3 through 5.3.5, the XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application. Version 5.3.6 fixes the issue. As a workaround, avoid using DOCTYPE parsing by `processEntities: false` option.

CVSS
7.5
EPSS
0.84%
54.4% percentile
CISA KEV
Not listed
Published
2026.02.20
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.84%
Technical severityCVSS 7.5

Vulnerability overview

fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. In versions 4.1.3 through 5.3.5, the XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application. Version 5.3.6 fixes the issue. As a workaround, avoid using DOCTYPE parsing by `processEntities: false` option.

Affected product and versions

Product
NaturalIntelligence fast-xml-parser, Red Hat Advanced Cluster Security 4.8, Red Hat Advanced Cluster Security 4.9
Affected versions
>= >= 5.0.0, < 5.3.6, >= >= 4.1.3, < 4.5.4, >= 4.1.3 < 5.3.6
Fixed versions
5.3.6

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that NaturalIntelligence fast-xml-parser, Red Hat Advanced Cluster Security 4.8, Red Hat Advanced Cluster Security 4.9 and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE
CWE-776